Authors:

S.A. Sabbagh(Columbia U.)

J.W. Berkery(Columbia U.)

J.M. Bialek(Columbia U.)

L. Delgado-Aparicio(JHU)

K. Tritz(JHU)

R.E. Bell(PPPL)

S.P. Gerhardt(PPPL)

B. LeBlanc(PPPL)

Resistive wall mode (RWM) research has focused on the behavior
and control
of the least stable mode. However, at sufficiently high
normalized beta,
multi-mode theory suggests that stable modes may significantly
influence the
plasma dynamics. [1] This may affect active RWM control
reliability in high
beta plasmas. [2] Experiments at very high normalized beta have been
conducted in NSTX to search for direct evidence of multi-mode RWM
dynamics.
Discharges were created with normalized beta reaching 7.4 in
conditions with
the ideal MHD no-wall limit near 4. Evidence of stable RWMs is
examined by
both kinetic and magnetic means. Characteristics are consistent
with RWM
behavior. At sufficiently high normalized beta, stable RWM-level low
frequency activity is observed. X-ray data amplitude depends on
beta, shows
the activity to be global, and propagates in the co-NBI direction at
frequencies near the expected peak in resonant magnetic field
amplification.
Observed growing RWMs appear to be separate from the stable mode
activity,
with different radial extent, supporting the hypothesis of
multiple modes.
[1] A.H. Boozer, Phys. Plasmas \textbf{10} (2003) 1458.
[2] S.A. Sabbagh, et al., Phys. Rev. Lett. \textbf{97} (2006) 045004.

*Work supported by U.S. DOE Contracts DE-FG02-99ER54524 and DE-AC02-09CH11466.

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2009.DPP.JO4.10